text: //===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
  //
  //                     The LLVM37 Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This family of functions perform manipulations on basic blocks, and
  // instructions contained within basic blocks.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm37/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm37/Analysis/AliasAnalysis.h"
  #include "llvm37/Analysis/CFG.h"
  #include "llvm37/Analysis/LoopInfo.h"
  #include "llvm37/Analysis/MemoryDependenceAnalysis.h"
  #include "llvm37/IR/Constant.h"
  #include "llvm37/IR/DataLayout.h"
  #include "llvm37/IR/Dominators.h"
  #include "llvm37/IR/Function.h"
  #include "llvm37/IR/Instructions.h"
  #include "llvm37/IR/IntrinsicInst.h"
  #include "llvm37/IR/Type.h"
  #include "llvm37/IR/ValueHandle.h"
  #include "llvm37/Support/ErrorHandling.h"
  #include "llvm37/Transforms/Scalar.h"
  #include "llvm37/Transforms/Utils/Local.h"
  #include <algorithm>
  using namespace llvm37;
  
  /// DeleteDeadBlock - Delete the specified block, which must have no
  /// predecessors.
  void llvm37::DeleteDeadBlock(BasicBlock *BB) {
    assert((pred_begin(BB) == pred_end(BB) ||
           // Can delete self loop.
           BB->getSinglePredecessor() == BB) && "Block is not dead!");
    TerminatorInst *BBTerm = BB->getTerminator();
  
    // Loop through all of our successors and make sure they know that one
    // of their predecessors is going away.
    for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i)
      BBTerm->getSuccessor(i)->removePredecessor(BB);
  
    // Zap all the instructions in the block.
    while (!BB->empty()) {
      Instruction &I = BB->back();
      // If this instruction is used, replace uses with an arbitrary value.
      // Because control flow can't get here, we don't care what we replace the
      // value with.  Note that since this block is unreachable, and all values
      // contained within it must dominate their uses, that all uses will
      // eventually be removed (they are themselves dead).
      if (!I.use_empty())
        I.replaceAllUsesWith(UndefValue::get(I.getType()));
      BB->getInstList().pop_back();
    }
  
    // Zap the block!
    BB->eraseFromParent();
  }
  
  /// FoldSingleEntryPHINodes - We know that BB has one predecessor.  If there are
  /// any single-entry PHI nodes in it, fold them away.  This handles the case
  /// when all entries to the PHI nodes in a block are guaranteed equal, such as
  /// when the block has exactly one predecessor.
  void llvm37::FoldSingleEntryPHINodes(BasicBlock *BB, AliasAnalysis *AA,
                                     MemoryDependenceAnalysis *MemDep) {
    if (!isa<PHINode>(BB->begin())) return;
  
    while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
      if (PN->getIncomingValue(0) != PN)
        PN->replaceAllUsesWith(PN->getIncomingValue(0));
      else
        PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
  
      if (MemDep)
        MemDep->removeInstruction(PN);  // Memdep updates AA itself.
      else if (AA && isa<PointerType>(PN->getType()))
        AA->deleteValue(PN);
  
      PN->eraseFromParent();
    }
  }
  
  
  /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
  /// is dead. Also recursively delete any operands that become dead as
  /// a result. This includes tracing the def-use list from the PHI to see if
  /// it is ultimately unused or if it reaches an unused cycle.
  bool llvm37::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
    // Recursively deleting a PHI may cause multiple PHIs to be deleted
    // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
    SmallVector<WeakVH, 8> PHIs;
    for (BasicBlock::iterator I = BB->begin();
         PHINode *PN = dyn_cast<PHINode>(I); ++I)
      PHIs.push_back(PN);
  
    bool Changed = false;
    for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
      if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
        Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
  
    return Changed;
  }
  
  /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
  /// if possible.  The return value indicates success or failure.
  bool llvm37::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
                                       LoopInfo *LI, AliasAnalysis *AA,
                                       MemoryDependenceAnalysis *MemDep) {
    // Don't merge away blocks who have their address taken.
    if (BB->hasAddressTaken()) return false;
  
    // Can't merge if there are multiple predecessors, or no predecessors.
    BasicBlock *PredBB = BB->getUniquePredecessor();
    if (!PredBB) return false;
  
    // Don't break self-loops.
    if (PredBB == BB) return false;
    // Don't break invokes.
    if (isa<InvokeInst>(PredBB->getTerminator())) return false;
  
    succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
    BasicBlock *OnlySucc = BB;
    for (; SI != SE; ++SI)
      if (*SI != OnlySucc) {
        OnlySucc = nullptr;     // There are multiple distinct successors!
        break;
      }
  
    // Can't merge if there are multiple successors.
    if (!OnlySucc) return false;
  
    // Can't merge if there is PHI loop.
    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
      if (PHINode *PN = dyn_cast<PHINode>(BI)) {
        for (Value *IncValue : PN->incoming_values())
          if (IncValue == PN)
            return false;
      } else
        break;
    }
  
    // Begin by getting rid of unneeded PHIs.
    if (isa<PHINode>(BB->front()))
      FoldSingleEntryPHINodes(BB, AA, MemDep);
  
    // Delete the unconditional branch from the predecessor...
    PredBB->getInstList().pop_back();
  
    // Make all PHI nodes that referred to BB now refer to Pred as their
    // source...
    BB->replaceAllUsesWith(PredBB);
  
    // Move all definitions in the successor to the predecessor...
    PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
  
    // Inherit predecessors name if it exists.
    if (!PredBB->hasName())
      PredBB->takeName(BB);
  
    // Finally, erase the old block and update dominator info.
    if (DT)
      if (DomTreeNode *DTN = DT->getNode(BB)) {
        DomTreeNode *PredDTN = DT->getNode(PredBB);
        SmallVector<DomTreeNode *, 8> Children(DTN->begin(), DTN->end());
        for (SmallVectorImpl<DomTreeNode *>::iterator DI = Children.begin(),
                                                      DE = Children.end();
             DI != DE; ++DI)
          DT->changeImmediateDominator(*DI, PredDTN);
  
        DT->eraseNode(BB);
      }
  
    if (LI)
      LI->removeBlock(BB);
  
    if (MemDep)
      MemDep->invalidateCachedPredecessors();
  
    BB->eraseFromParent();
    return true;
  }
  
  /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
  /// with a value, then remove and delete the original instruction.
  ///
  void llvm37::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
                                  BasicBlock::iterator &BI, Value *V) {
    Instruction &I = *BI;
    // Replaces all of the uses of the instruction with uses of the value
    I.replaceAllUsesWith(V);
  
    // Make sure to propagate a name if there is one already.
    if (I.hasName() && !V->hasName())
      V->takeName(&I);
  
    // Delete the unnecessary instruction now...
    BI = BIL.erase(BI);
  }
  
  
  /// ReplaceInstWithInst - Replace the instruction specified by BI with the
  /// instruction specified by I.  The original instruction is deleted and BI is
  /// updated to point to the new instruction.
  ///
  void llvm37::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
                                 BasicBlock::iterator &BI, Instruction *I) {
    assert(I->getParent() == nullptr &&
           "ReplaceInstWithInst: Instruction already inserted into basic block!");
  
    // Copy debug location to newly added instruction, if it wasn't already set
    // by the caller.
    if (!I->getDebugLoc())
      I->setDebugLoc(BI->getDebugLoc());
  
    // Insert the new instruction into the basic block...
    BasicBlock::iterator New = BIL.insert(BI, I);
  
    // Replace all uses of the old instruction, and delete it.
    ReplaceInstWithValue(BIL, BI, I);
  
    // Move BI back to point to the newly inserted instruction
    BI = New;
  }
  
  /// ReplaceInstWithInst - Replace the instruction specified by From with the
  /// instruction specified by To.
  ///
  void llvm37::ReplaceInstWithInst(Instruction *From, Instruction *To) {
    BasicBlock::iterator BI(From);
    ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
  }
  
  /// SplitEdge -  Split the edge connecting specified block. Pass P must
  /// not be NULL.
  BasicBlock *llvm37::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
                              LoopInfo *LI) {
    unsigned SuccNum = GetSuccessorNumber(BB, Succ);
  
    // If this is a critical edge, let SplitCriticalEdge do it.
    TerminatorInst *LatchTerm = BB->getTerminator();
    if (SplitCriticalEdge(LatchTerm, SuccNum, CriticalEdgeSplittingOptions(DT, LI)
                                                  .setPreserveLCSSA()))
      return LatchTerm->getSuccessor(SuccNum);
  
    // If the edge isn't critical, then BB has a single successor or Succ has a
    // single pred.  Split the block.
    if (BasicBlock *SP = Succ->getSinglePredecessor()) {
      // If the successor only has a single pred, split the top of the successor
      // block.
      assert(SP == BB && "CFG broken");
      SP = nullptr;
      return SplitBlock(Succ, Succ->begin(), DT, LI);
    }
  
    // Otherwise, if BB has a single successor, split it at the bottom of the
    // block.
    assert(BB->getTerminator()->getNumSuccessors() == 1 &&
           "Should have a single succ!");
    return SplitBlock(BB, BB->getTerminator(), DT, LI);
  }
  
  unsigned
  llvm37::SplitAllCriticalEdges(Function &F,
                              const CriticalEdgeSplittingOptions &Options) {
    unsigned NumBroken = 0;
    for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
      TerminatorInst *TI = I->getTerminator();
      if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
        for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
          if (SplitCriticalEdge(TI, i, Options))
            ++NumBroken;
    }
    return NumBroken;
  }
  
  /// SplitBlock - Split the specified block at the specified instruction - every
  /// thing before SplitPt stays in Old and everything starting with SplitPt moves
  /// to a new block.  The two blocks are joined by an unconditional branch and
  /// the loop info is updated.
  ///
  BasicBlock *llvm37::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
                               DominatorTree *DT, LoopInfo *LI) {
    BasicBlock::iterator SplitIt = SplitPt;
    while (isa<PHINode>(SplitIt) || isa<LandingPadInst>(SplitIt))
      ++SplitIt;
    BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
  
    // The new block lives in whichever loop the old one did. This preserves
    // LCSSA as well, because we force the split point to be after any PHI nodes.
    if (LI)
      if (Loop *L = LI->getLoopFor(Old))
        L->addBasicBlockToLoop(New, *LI);
  
    if (DT)
      // Old dominates New. New node dominates all other nodes dominated by Old.
      if (DomTreeNode *OldNode = DT->getNode(Old)) {
        std::vector<DomTreeNode *> Children;
        for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
             I != E; ++I)
          Children.push_back(*I);
  
        DomTreeNode *NewNode = DT->addNewBlock(New, Old);
        for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
               E = Children.end(); I != E; ++I)
          DT->changeImmediateDominator(*I, NewNode);
      }
  
    return New;
  }
  
  /// UpdateAnalysisInformation - Update DominatorTree, LoopInfo, and LCCSA
  /// analysis information.
  static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
                                        ArrayRef<BasicBlock *> Preds,
                                        DominatorTree *DT, LoopInfo *LI,
                                        bool PreserveLCSSA, bool &HasLoopExit) {
    // Update dominator tree if available.
    if (DT)
      DT->splitBlock(NewBB);
  
    // The rest of the logic is only relevant for updating the loop structures.
    if (!LI)
      return;
  
    Loop *L = LI->getLoopFor(OldBB);
  
    // If we need to preserve loop analyses, collect some information about how
    // this split will affect loops.
    bool IsLoopEntry = !!L;
    bool SplitMakesNewLoopHeader = false;
    for (ArrayRef<BasicBlock *>::iterator i = Preds.begin(), e = Preds.end();
         i != e; ++i) {
      BasicBlock *Pred = *i;
  
      // If we need to preserve LCSSA, determine if any of the preds is a loop
      // exit.
      if (PreserveLCSSA)
        if (Loop *PL = LI->getLoopFor(Pred))
          if (!PL->contains(OldBB))
            HasLoopExit = true;
  
      // If we need to preserve LoopInfo, note whether any of the preds crosses
      // an interesting loop boundary.
      if (!L)
        continue;
      if (L->contains(Pred))
        IsLoopEntry = false;
      else
        SplitMakesNewLoopHeader = true;
    }
  
    // Unless we have a loop for OldBB, nothing else to do here.
    if (!L)
      return;
  
    if (IsLoopEntry) {
      // Add the new block to the nearest enclosing loop (and not an adjacent
      // loop). To find this, examine each of the predecessors and determine which
      // loops enclose them, and select the most-nested loop which contains the
      // loop containing the block being split.
      Loop *InnermostPredLoop = nullptr;
      for (ArrayRef<BasicBlock*>::iterator
             i = Preds.begin(), e = Preds.end(); i != e; ++i) {
        BasicBlock *Pred = *i;
        if (Loop *PredLoop = LI->getLoopFor(Pred)) {
          // Seek a loop which actually contains the block being split (to avoid
          // adjacent loops).
          while (PredLoop && !PredLoop->contains(OldBB))
            PredLoop = PredLoop->getParentLoop();
  
          // Select the most-nested of these loops which contains the block.
          if (PredLoop && PredLoop->contains(OldBB) &&
              (!InnermostPredLoop ||
               InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
            InnermostPredLoop = PredLoop;
        }
      }
  
      if (InnermostPredLoop)
        InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
    } else {
      L->addBasicBlockToLoop(NewBB, *LI);
      if (SplitMakesNewLoopHeader)
        L->moveToHeader(NewBB);
    }
  }
  
  /// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming
  /// from NewBB. This also updates AliasAnalysis, if available.
  static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
                             ArrayRef<BasicBlock *> Preds, BranchInst *BI,
                             AliasAnalysis *AA, bool HasLoopExit) {
    // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
    SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
    for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
      PHINode *PN = cast<PHINode>(I++);
  
      // Check to see if all of the values coming in are the same.  If so, we
      // don't need to create a new PHI node, unless it's needed for LCSSA.
      Value *InVal = nullptr;
      if (!HasLoopExit) {
        InVal = PN->getIncomingValueForBlock(Preds[0]);
        for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
          if (!PredSet.count(PN->getIncomingBlock(i)))
            continue;
          if (!InVal)
            InVal = PN->getIncomingValue(i);
          else if (InVal != PN->getIncomingValue(i)) {
            InVal = nullptr;
            break;
          }
        }
      }
  
      if (InVal) {
        // If all incoming values for the new PHI would be the same, just don't
        // make a new PHI.  Instead, just remove the incoming values from the old
        // PHI.
  
        // NOTE! This loop walks backwards for a reason! First off, this minimizes
        // the cost of removal if we end up removing a large number of values, and
        // second off, this ensures that the indices for the incoming values
        // aren't invalidated when we remove one.
        for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
          if (PredSet.count(PN->getIncomingBlock(i)))
            PN->removeIncomingValue(i, false);
  
        // Add an incoming value to the PHI node in the loop for the preheader
        // edge.
        PN->addIncoming(InVal, NewBB);
        continue;
      }
  
      // If the values coming into the block are not the same, we need a new
      // PHI.
      // Create the new PHI node, insert it into NewBB at the end of the block
      PHINode *NewPHI =
          PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
  
      // NOTE! This loop walks backwards for a reason! First off, this minimizes
      // the cost of removal if we end up removing a large number of values, and
      // second off, this ensures that the indices for the incoming values aren't
      // invalidated when we remove one.
      for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
        BasicBlock *IncomingBB = PN->getIncomingBlock(i);
        if (PredSet.count(IncomingBB)) {
          Value *V = PN->removeIncomingValue(i, false);
          NewPHI->addIncoming(V, IncomingBB);
        }
      }
  
      PN->addIncoming(NewPHI, NewBB);
    }
  }
  
  /// SplitBlockPredecessors - This method introduces at least one new basic block
  /// into the function and moves some of the predecessors of BB to be
  /// predecessors of the new block. The new predecessors are indicated by the
  /// Preds array. The new block is given a suffix of 'Suffix'. Returns new basic
  /// block to which predecessors from Preds are now pointing.
  ///
  /// If BB is a landingpad block then additional basicblock might be introduced.
  /// It will have suffix of 'Suffix'+".split_lp".
  /// See SplitLandingPadPredecessors for more details on this case.
  ///
  /// This currently updates the LLVM37 IR, AliasAnalysis, DominatorTree,
  /// LoopInfo, and LCCSA but no other analyses. In particular, it does not
  /// preserve LoopSimplify (because it's complicated to handle the case where one
  /// of the edges being split is an exit of a loop with other exits).
  ///
  BasicBlock *llvm37::SplitBlockPredecessors(BasicBlock *BB,
                                           ArrayRef<BasicBlock *> Preds,
                                           const char *Suffix, AliasAnalysis *AA,
                                           DominatorTree *DT, LoopInfo *LI,
                                           bool PreserveLCSSA) {
    // For the landingpads we need to act a bit differently.
    // Delegate this work to the SplitLandingPadPredecessors.
    if (BB->isLandingPad()) {
      SmallVector<BasicBlock*, 2> NewBBs;
      std::string NewName = std::string(Suffix) + ".split-lp";
  
      SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(),
                                  NewBBs, AA, DT, LI, PreserveLCSSA);
      return NewBBs[0];
    }
  
    // Create new basic block, insert right before the original block.
    BasicBlock *NewBB = BasicBlock::Create(
        BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
  
    // The new block unconditionally branches to the old block.
    BranchInst *BI = BranchInst::Create(BB, NewBB);
    BI->setDebugLoc(BB->getFirstNonPHI()->getDebugLoc());
  
    // Move the edges from Preds to point to NewBB instead of BB.
    for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
      // This is slightly more strict than necessary; the minimum requirement
      // is that there be no more than one indirectbr branching to BB. And
      // all BlockAddress uses would need to be updated.
      assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
             "Cannot split an edge from an IndirectBrInst");
      Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
    }
  
    // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
    // node becomes an incoming value for BB's phi node.  However, if the Preds
    // list is empty, we need to insert dummy entries into the PHI nodes in BB to
    // account for the newly created predecessor.
    if (Preds.size() == 0) {
      // Insert dummy values as the incoming value.
      for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
        cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
      return NewBB;
    }
  
    // Update DominatorTree, LoopInfo, and LCCSA analysis information.
    bool HasLoopExit = false;
    UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, PreserveLCSSA,
                              HasLoopExit);
  
    // Update the PHI nodes in BB with the values coming from NewBB.
    UpdatePHINodes(BB, NewBB, Preds, BI, AA, HasLoopExit);
    return NewBB;
  }
  
  /// SplitLandingPadPredecessors - This method transforms the landing pad,
  /// OrigBB, by introducing two new basic blocks into the function. One of those
  /// new basic blocks gets the predecessors listed in Preds. The other basic
  /// block gets the remaining predecessors of OrigBB. The landingpad instruction
  /// OrigBB is clone into both of the new basic blocks. The new blocks are given
  /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
  ///
  /// This currently updates the LLVM37 IR, AliasAnalysis, DominatorTree,
  /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
  /// it does not preserve LoopSimplify (because it's complicated to handle the
  /// case where one of the edges being split is an exit of a loop with other
  /// exits).
  ///
  void llvm37::SplitLandingPadPredecessors(BasicBlock *OrigBB,
                                         ArrayRef<BasicBlock *> Preds,
                                         const char *Suffix1, const char *Suffix2,
                                         SmallVectorImpl<BasicBlock *> &NewBBs,
                                         AliasAnalysis *AA, DominatorTree *DT,
                                         LoopInfo *LI, bool PreserveLCSSA) {
    assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
  
    // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
    // it right before the original block.
    BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
                                            OrigBB->getName() + Suffix1,
                                            OrigBB->getParent(), OrigBB);
    NewBBs.push_back(NewBB1);
  
    // The new block unconditionally branches to the old block.
    BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
    BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
  
    // Move the edges from Preds to point to NewBB1 instead of OrigBB.
    for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
      // This is slightly more strict than necessary; the minimum requirement
      // is that there be no more than one indirectbr branching to BB. And
      // all BlockAddress uses would need to be updated.
      assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
             "Cannot split an edge from an IndirectBrInst");
      Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
    }
  
    bool HasLoopExit = false;
    UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, PreserveLCSSA,
                              HasLoopExit);
  
    // Update the PHI nodes in OrigBB with the values coming from NewBB1.
    UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, AA, HasLoopExit);
  
    // Move the remaining edges from OrigBB to point to NewBB2.
    SmallVector<BasicBlock*, 8> NewBB2Preds;
    for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
         i != e; ) {
      BasicBlock *Pred = *i++;
      if (Pred == NewBB1) continue;
      assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
             "Cannot split an edge from an IndirectBrInst");
      NewBB2Preds.push_back(Pred);
      e = pred_end(OrigBB);
    }
  
    BasicBlock *NewBB2 = nullptr;
    if (!NewBB2Preds.empty()) {
      // Create another basic block for the rest of OrigBB's predecessors.
      NewBB2 = BasicBlock::Create(OrigBB->getContext(),
                                  OrigBB->getName() + Suffix2,
                                  OrigBB->getParent(), OrigBB);
      NewBBs.push_back(NewBB2);
  
      // The new block unconditionally branches to the old block.
      BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
      BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
  
      // Move the remaining edges from OrigBB to point to NewBB2.
      for (SmallVectorImpl<BasicBlock*>::iterator
             i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i)
        (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
  
      // Update DominatorTree, LoopInfo, and LCCSA analysis information.
      HasLoopExit = false;
      UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI,
                                PreserveLCSSA, HasLoopExit);
  
      // Update the PHI nodes in OrigBB with the values coming from NewBB2.
      UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, AA, HasLoopExit);
    }
  
    LandingPadInst *LPad = OrigBB->getLandingPadInst();
    Instruction *Clone1 = LPad->clone();
    Clone1->setName(Twine("lpad") + Suffix1);
    NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
  
    if (NewBB2) {
      Instruction *Clone2 = LPad->clone();
      Clone2->setName(Twine("lpad") + Suffix2);
      NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
  
      // Create a PHI node for the two cloned landingpad instructions.
      PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
      PN->addIncoming(Clone1, NewBB1);
      PN->addIncoming(Clone2, NewBB2);
      LPad->replaceAllUsesWith(PN);
      LPad->eraseFromParent();
    } else {
      // There is no second clone. Just replace the landing pad with the first
      // clone.
      LPad->replaceAllUsesWith(Clone1);
      LPad->eraseFromParent();
    }
  }
  
  /// FoldReturnIntoUncondBranch - This method duplicates the specified return
  /// instruction into a predecessor which ends in an unconditional branch. If
  /// the return instruction returns a value defined by a PHI, propagate the
  /// right value into the return. It returns the new return instruction in the
  /// predecessor.
  ReturnInst *llvm37::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
                                               BasicBlock *Pred) {
    Instruction *UncondBranch = Pred->getTerminator();
    // Clone the return and add it to the end of the predecessor.
    Instruction *NewRet = RI->clone();
    Pred->getInstList().push_back(NewRet);
  
    // If the return instruction returns a value, and if the value was a
    // PHI node in "BB", propagate the right value into the return.
    for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
         i != e; ++i) {
      Value *V = *i;
      Instruction *NewBC = nullptr;
      if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
        // Return value might be bitcasted. Clone and insert it before the
        // return instruction.
        V = BCI->getOperand(0);
        NewBC = BCI->clone();
        Pred->getInstList().insert(NewRet, NewBC);
        *i = NewBC;
      }
      if (PHINode *PN = dyn_cast<PHINode>(V)) {
        if (PN->getParent() == BB) {
          if (NewBC)
            NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
          else
            *i = PN->getIncomingValueForBlock(Pred);
        }
      }
    }
  
    // Update any PHI nodes in the returning block to realize that we no
    // longer branch to them.
    BB->removePredecessor(Pred);
    UncondBranch->eraseFromParent();
    return cast<ReturnInst>(NewRet);
  }
  
  /// SplitBlockAndInsertIfThen - Split the containing block at the
  /// specified instruction - everything before and including SplitBefore stays
  /// in the old basic block, and everything after SplitBefore is moved to a
  /// new block. The two blocks are connected by a conditional branch
  /// (with value of Cmp being the condition).
  /// Before:
  ///   Head
  ///   SplitBefore
  ///   Tail
  /// After:
  ///   Head
  ///   if (Cond)
  ///     ThenBlock
  ///   SplitBefore
  ///   Tail
  ///
  /// If Unreachable is true, then ThenBlock ends with
  /// UnreachableInst, otherwise it branches to Tail.
  /// Returns the NewBasicBlock's terminator.
  
  TerminatorInst *llvm37::SplitBlockAndInsertIfThen(Value *Cond,
                                                  Instruction *SplitBefore,
                                                  bool Unreachable,
                                                  MDNode *BranchWeights,
                                                  DominatorTree *DT) {
    BasicBlock *Head = SplitBefore->getParent();
    BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
    TerminatorInst *HeadOldTerm = Head->getTerminator();
    LLVM37Context &C = Head->getContext();
    BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
    TerminatorInst *CheckTerm;
    if (Unreachable)
      CheckTerm = new UnreachableInst(C, ThenBlock);
    else
      CheckTerm = BranchInst::Create(Tail, ThenBlock);
    CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
    BranchInst *HeadNewTerm =
      BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
    HeadNewTerm->setMetadata(LLVM37Context::MD_prof, BranchWeights);
    ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
  
    if (DT) {
      if (DomTreeNode *OldNode = DT->getNode(Head)) {
        std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
  
        DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
        for (auto Child : Children)
          DT->changeImmediateDominator(Child, NewNode);
  
        // Head dominates ThenBlock.
        DT->addNewBlock(ThenBlock, Head);
      }
    }
  
    return CheckTerm;
  }
  
  /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
  /// but also creates the ElseBlock.
  /// Before:
  ///   Head
  ///   SplitBefore
  ///   Tail
  /// After:
  ///   Head
  ///   if (Cond)
  ///     ThenBlock
  ///   else
  ///     ElseBlock
  ///   SplitBefore
  ///   Tail
  void llvm37::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
                                           TerminatorInst **ThenTerm,
                                           TerminatorInst **ElseTerm,
                                           MDNode *BranchWeights) {
    BasicBlock *Head = SplitBefore->getParent();
    BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
    TerminatorInst *HeadOldTerm = Head->getTerminator();
    LLVM37Context &C = Head->getContext();
    BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
    BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
    *ThenTerm = BranchInst::Create(Tail, ThenBlock);
    (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
    *ElseTerm = BranchInst::Create(Tail, ElseBlock);
    (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
    BranchInst *HeadNewTerm =
      BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
    HeadNewTerm->setMetadata(LLVM37Context::MD_prof, BranchWeights);
    ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
  }
  
  
  /// GetIfCondition - Given a basic block (BB) with two predecessors,
  /// check to see if the merge at this block is due
  /// to an "if condition".  If so, return the boolean condition that determines
  /// which entry into BB will be taken.  Also, return by references the block
  /// that will be entered from if the condition is true, and the block that will
  /// be entered if the condition is false.
  ///
  /// This does no checking to see if the true/false blocks have large or unsavory
  /// instructions in them.
  Value *llvm37::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
                               BasicBlock *&IfFalse) {
    PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
    BasicBlock *Pred1 = nullptr;
    BasicBlock *Pred2 = nullptr;
  
    if (SomePHI) {
      if (SomePHI->getNumIncomingValues() != 2)
        return nullptr;
      Pred1 = SomePHI->getIncomingBlock(0);
      Pred2 = SomePHI->getIncomingBlock(1);
    } else {
      pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
      if (PI == PE) // No predecessor
        return nullptr;
      Pred1 = *PI++;
      if (PI == PE) // Only one predecessor
        return nullptr;
      Pred2 = *PI++;
      if (PI != PE) // More than two predecessors
        return nullptr;
    }
  
    // We can only handle branches.  Other control flow will be lowered to
    // branches if possible anyway.
    BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
    BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
    if (!Pred1Br || !Pred2Br)
      return nullptr;
  
    // Eliminate code duplication by ensuring that Pred1Br is conditional if
    // either are.
    if (Pred2Br->isConditional()) {
      // If both branches are conditional, we don't have an "if statement".  In
      // reality, we could transform this case, but since the condition will be
      // required anyway, we stand no chance of eliminating it, so the xform is
      // probably not profitable.
      if (Pred1Br->isConditional())
        return nullptr;
  
      std::swap(Pred1, Pred2);
      std::swap(Pred1Br, Pred2Br);
    }
  
    if (Pred1Br->isConditional()) {
      // The only thing we have to watch out for here is to make sure that Pred2
      // doesn't have incoming edges from other blocks.  If it does, the condition
      // doesn't dominate BB.
      if (!Pred2->getSinglePredecessor())
        return nullptr;
  
      // If we found a conditional branch predecessor, make sure that it branches
      // to BB and Pred2Br.  If it doesn't, this isn't an "if statement".
      if (Pred1Br->getSuccessor(0) == BB &&
          Pred1Br->getSuccessor(1) == Pred2) {
        IfTrue = Pred1;
        IfFalse = Pred2;
      } else if (Pred1Br->getSuccessor(0) == Pred2 &&
                 Pred1Br->getSuccessor(1) == BB) {
        IfTrue = Pred2;
        IfFalse = Pred1;
      } else {
        // We know that one arm of the conditional goes to BB, so the other must
        // go somewhere unrelated, and this must not be an "if statement".
        return nullptr;
      }
  
      return Pred1Br->getCondition();
    }
  
    // Ok, if we got here, both predecessors end with an unconditional branch to
    // BB.  Don't panic!  If both blocks only have a single (identical)
    // predecessor, and THAT is a conditional branch, then we're all ok!
    BasicBlock *CommonPred = Pred1->getSinglePredecessor();
    if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
      return nullptr;
  
    // Otherwise, if this is a conditional branch, then we can use it!
    BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
    if (!BI) return nullptr;
  
    assert(BI->isConditional() && "Two successors but not conditional?");
    if (BI->getSuccessor(0) == Pred1) {
      IfTrue = Pred1;
      IfFalse = Pred2;
    } else {
      IfTrue = Pred2;
      IfFalse = Pred1;
    }
    return BI->getCondition();
  }
  